Photons corrections

Olivier Deschamps LPC Clermont-Fd

CaloSoft meeting May 2004 LHCb week

1

Photons corrections

LHCb CaloSoft meeting – 25 May 2004

Olivier Deschamps

LPC-Clermont



2

Remind

Photon corrections (E-/S-/L-corrections) for DC04 were evaluated in February 2004 using PGUN-produced γ/π° samples (Gauss v14r1 - Geant4 bugged - v6r0) and introduced in Brunel v23r3.

Study of pre-produced DC04 data (Geant4 v6r1) shows a bad behaviour for neutrals

-> Miscalibration reported in B->K*γ and B->π-π+π° selections

-> bad electron identification

Patrick reports a 7.2% Ecal energy shift between Geant4 v6r0 and v6r1 (origin unknown)

Photon corrections re-evaluated using PGUN sample (G4 v6r1).



3

Data sample

• Roughly mimics photon from radiative B decay

• Gauss v15r6 - Boole v5r8 – Brunel v23r7

ActiveToTotal

May-DC04 7.84 (Geant4 v6r1)

February-DC04 8.4 (Geant4 v6r0)

January-DC04 10.5 (bad evaluation)

DC03 7.5 (Geant3)

Use samples of single photons produced with PGUN

Discrete energy & acceptance samples:

Energy : 5.0 10.0 16.8 33.8 50.0 100.0 168.0 GeV

InnerMiddleOuter

K*γ

Pgun γ



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E/S/L corrections

• New correction parameters not drastically different from february one.

• With february data the transversal shower shape was found to be smaller by 10-15% wrt DC03 value.

S-shape parameter now slightly re-increases (but not at the level of DC03)

• Rough feeling : new corrections are in between February and DC03 corrections

• Main effect is the 7.2% energy miscalibration



5

Energy correction

3x3 measured energy versus PGUN energy

Leakage at high energy was not observed with february data

backward leakage



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Energy correction

3x3 measured energy versus relative barycenter position

Strange behaviour already observed with february data

E3

x3/E

γ

barycenter-center distance (cell size unit)

Outer Ecal Inner Ecal



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Energy resolution

No Spd hit(« unconverted »)

Spd hit (« converted »)

No Spd No Ps

1/√E (GeV1/2)

σE/E

(%

)

Spread ΔE/σ

E

MeV)5165()%02.037.1(

E

)%1.05.11(

EE

Overall :

Similar to february performance



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Energy resolution : DC04 versus DC03

E

MeV)4160()%02.037.1(

E

)%1.04.11(

EE

E

MeV)662()%08.022.1(

E

)%5.03.10(

EE

DC03 PGUN photons

DC04 PGUN photonsUnconverted photons (No SPD hit)



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Angular resolution

No Spd hit(« unconverted »)

Spd hit (« converted »)

No Spd No Ps

1/√E (GeV1/2)

σΘ/Θ

(%

)

)%01.019.0(E

)%1.065.0(

Overall :

Inner

Middle

Outer

Similar to february performance

Warning : average resolutions ! Here PGUN distribution is used !

1/√E (GeV1/2)



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Angular resolution

Angular spread ΔΘ/σ

Polar angle spread badly fitwith a single-gaussian function

2 gaussians slightly displaced

Angular resolution should be improved



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Resolved and merged π0s

Resolved Merged

Performance seems OK

Neutral pions from PGUN production



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Software implementation

• Because DC04 production being started, new corrections to be applied at the DaVinci level (as done in 2003 for TDR data)

• Will be available with the next DaVinci release (v11r8)

• Preliminary checks performed on B→K*γ and B→ 3π selections (see Tuesday meeting last week)

- B mass resolution and selection yield seems OK for B → 3π

- Galina reported a degradated B mass

resolution for K*γ wrt TDR (however the mass peak

is correctly located)

σ(K*γ)~ 75 MeV/c² (TDR 2003 : 64 MeV/c²)

Degradation more important for converted (SPD)

photons



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Check energy resolution

Pgun (single photon events) versus photon from K*γ (full events)

PGUN

K*γ

Converted (SPD) photons only

Energy resolution slightly degradated in full events. No dramatic effect with converted photons.

Energy spread (EMC-E)/σσE(E) from PGUN

Energy spread (EMC-E)/σ



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Check angular resolution

Pgun (single photon events) versus photon from K*γ (full events)

PGUN

K*γ

Converted (SPD) photons only

Angular resolution slightly degradated in full events. No dramatic effect with converted photons.

Angular spread (Θ-ΘMC)/σσΘ(E) from PGUN

Angular spread (Θ-ΘMC)/σ



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Inner hole effect

PGUN photon well produced in Ecal acceptanceLow angle photon from K*γ (Θ<40 mrad) versus larger

acceptance

PGUN

K*γ

Large systematic effect on photon direction near inner hole. Low angle photons represent ~ 15% of total.Inner hole acceptance changed this year. May (partially) explain Galina’s results ?

Energy spread (EMC-E)/σσΘ(E) from PGUN

Angular spread (Θ -ΘMC)/σ



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Boundary effect

Inner Ecal

Middle Ecal

• Strange behaviour detected near Ecal boundaries : 3x3 cluster use more than 9 cells to compute energy and barycenter !!! Due to the use of the cell size to define neighbourhood.Some large cells are defined as neighboor of smaller size seed even if they arenot adjacent !!!

• Small piece of code added in DaVinci to correct for that.

• More efficient fix will be done next week (thanks to Vanya’s help)



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Photon origin spread effect

The spread of the photon origin (IP is 5 cm width gaussian) is NOT a negligible effect. Has to be taken into account to compare PGUN (originating from (0,0,0)) and collision events.

%4.0m 12.5

cm 5

z

z

0.5% m few

mm few

x

x

Impact of barycenter resolution :

Impact of IP spread (5cm) :

• PhotonParticleMaker compute photon momentum as originating from (0,0,0) • MergedPhoton originates from first found primary vertex• Photon direction re-evaluated according to B vertex position in K*γ selection • But not yet in B→3π (Arnaud will introduce it soon in selection)

Could be technically usefull to change ResolvedPi0 and MergedPi0Maker algorithmsas DaVinci tools allowing analysis dependent origin for neutral pions.



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Conclusions

• New photon corrections ready for DC04 production (to be applied on stripping).

• Available with the next DaVinci release.

• Performance similar to february corrections (and parameters almost).

• Performance degradated wrt DC03 using Geant3 (new Calo non-uniformities ?)

• Some imperfections remain :

- Ecal boundary effects (being fix)

- Inner hole border

- Limitation due to use of PGUN versus full events

- Partially overlap clusters reconstruction not re-evaluated

these imperfections was already present last year (can not explain degradation observed in K*γ by Galina)

•Some improvement should be possible



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Perspective

• On another hand MC-truth is used to correct for quite tiny effects

- Use of MC 4-momentum as reference

- Use of cleaned photon sample (cluster-photon associator)

• Need to trust Monte-Carlo !!

• Are the correction performance achievable ? (although currently non perfect !)

Could we extract refined E-correction from data ? S-shape ? L-correction ?

- Using neutral pion fit procedure à la Hera-B

- Using tracked electrons

• Try to develop new Ecal correction procedure for DC05 ...

Photons corrections

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